This invention relates to an optical device or article. More particularly, it relates to such an article or device including a molecularly oriented highly birefringent polymeric material.
Materials having a birefringent character have been variously applied in connection with the construction of filter and other optical devices. Frequently, a birefringent element utilized in an optical filter or other device will comprise a plate made from a monocrystalline form of birefringent material. Single crystals are expensive materials and are not readily formed to the desired shape or conformation required in particular applications. The size to which crystals can be grown represents an additional limitation on the utilization of such materials in optical devices.
Optical devices including a birefringent material in the form of a polymeric layer, such as may be formed by the unidirectional stretching of a suitable polymeric material, have also been described. Thus, light-polarizing devices utilizing a polymeric birefringent layer have been described in U.S. Pat. No. 3,213,753 (issued Oct. 26, 1965 to H. G. Rogers). Optical devices including polymeric birefringent materials have also been set forth, for example, in U.S. Pat. No. 3,506,333 (issued Apr. 14, 1970 to E. H. Land) and in U.S. Pat. No. 3,610,729 (issued Oct. 15, 1971 to H. G. Rogers). Frequently, the efficiency of an optical filter, polarizing or other optical device including a birefringent element or layer will depend upon the realization of large net differences in refractive index between a birefringent material and adjacent or contiguous layers. In general, such net differences will be maximized where a birefringent material is highly birefringent. Correspondingly, large net differences in refractive indices of contiguous layers will be unattainable where birefringent polymeric materials otherwise suited to application in an optical device tend to exhibit either low or only marginal birefringent character. Accordingly, optical devices including polymeric layers or elements exhibiting a highly birefringent character will be of particular interest for optical applications and enhanced efficiency.